The objectives of this study are to determine the relationship between plasma fenoldopam concentrations and blood pressure effects, to assess the maximally tolerated dose and a minimally effective dose, to determine if the effect of fenoldopam is maintained through a 48 hour infusion and to determine if pharmacokinetic parameters are altered by prolonged infusion. Fenoldopam is a potent systemic and renal vasodilator which stimulates post-synaptic dopamine (DA1).